1. Field of the Invention
The present invention relates to an electrostatic discharge (ESD) protection device used to protect semiconductor devices and electronic circuits from static electricity and a method for producing the ESD protection device. More specifically, the present invention relates to an ESD protection device including first and second discharge electrodes that face each other with a gap therebetween in a cavity and a method for producing the ESD protection device.
2. Description of the Related Art
Various ESD protection devices have been used to protect semiconductor devices and electronic circuits from static electricity.
For example, International Publication No. WO2008/146514 discloses an ESD protection device shown in FIGS. 5A and 5B. An ESD protection device 101 includes a ceramic multilayer substrate 102. The ceramic multilayer substrate 102 is made of glass ceramic, that is, low temperature co-fired ceramic (LTCC). A cavity 103 is provided in the ceramic multilayer substrate 102. A first discharge electrode 104 and a second discharge electrode 105 are disposed in the ceramic multilayer substrate 102. The respective edges of the first and second discharge electrodes 104 and 105 are located in the cavity 103. As shown in FIG. 5A, the edges of the first and second discharge electrodes 104 and 105 face each other with a gap G provided therebetween in the cavity 103. A mixture portion 106 is disposed on the lower surface of the cavity 103. The mixture portion 106 is in contact with the lower surfaces of the first and second discharge electrodes 104 and 105 so as to connect the first discharge electrode 104 with the second discharge electrode 105.
FIG. 5B shows the details of the mixture portion 106. In the mixture portion 106, conductive particles 106a coated with an inorganic material having no conductivity are dispersed in a ceramic material. The mixture portion 106 is disposed in order to easily achieve creeping discharge between the first and second discharge electrodes. Thus, the discharge starting voltage can be decreased. The mixture portion 106 functions as a discharge supporting electrode.
In the ESD protection device and the method for producing the ESD protection device disclosed in International Publication No. WO2008/146514, a glass ceramic substrate is fired while a material used to form a cavity is provided in the glass ceramic substrate. Therefore, when a cavity is formed by the elimination of the material used to form a cavity, glass included in the glass ceramic substrate sometimes enters the discharge supporting electrode, which is the mixture portion 106. As a result, an undesired short circuit is caused between the first and second discharge electrodes and, thus, the protection from static electricity cannot be achieved with certainty.